PROJECTSUMMARY?PROJECT3 Clinicianstreatingpatientsincommunitysettingsfacesignificantchallenges;?evidencecanbelackingforthe patientstheytypicallysee,particularlyforfrailelderlypeoplewhoareoftenexcludedfromrandomizedtrials, andcommunityhospitalsmaynotnecessarilyprovidethesamelevelofexpertiseasthelargeacademic medicalcenterswheretrialsoftentakeplace.Toaddressconcernsaboutthepotentialforpoorqualitycare, manyinstitutionsareusingrisk-adjustedperformancemeasures,butthereisconsiderableuncertaintyabout whethertheycanbeinterpretedinameaningfulwaygiventhepotentialforunmeasuredconfoundingand consequentbiases.Inthisproject,weuseacombinationoftrialdata,registrydata,andclaimsdata augmentedwithnatural-experiments,toaddresstheseconcernsalongthreedimensions.First,weharnessthe strengthofalargeregistry,theVascularQualityInitiativeforpatientswithlower-extremityperipheralvascular disease,toestimatetheextentofheterogeneityacrosspatients,andhospitals,intreatmenteffects;?weplanto validateourestimateswhenanongoingclinicaltrial(BEST-CLI)iscompleted.Second,weusetheentryand exitofhospitalsandphysicians,andtheconsequentimpactonpopulation-levelhealth,toassessthevalidityof ourproviderperformancemeasuresderivedfromclaims.Finally,weusethenaturalexperimentsofprovider entryandexittounderstandwhetherthesesuddenchangesaremoreburdensomeforvulnerablepopulations suchasminoritypatientsandthosewithadiagnosisofAlzheimer?sDiseaseandrelateddementia(ADRD). WebuildonkeystrengthsoftheNIAP01,includingextensiveMedicareclaimsdata,accesstoclinical registries,economicmodeling,andmostimportantlydetailedknowledgeoftheclinicalsettingthrough collaborationbetweencliniciansandsocialscientists.Thisprojectwillcontributetootherprojects(e.g.,4and 2),andhasthepotentialtosubstantiallyimprovepatientoutcomesbyimprovingguidelinesforpatientand hospitalchoice.